Nitrocellulose propellants containing lead salts of aliphatic acids



, temperature.

United States Patent INITROCELLULOSE PROPELLANT S CONTAININ LEAD SALTS FALIPHATIC ACIDS Robert: A. Cooley, East Alton, Ill., and Herman A.

Bruson, North Haven, Conn., assignors to Olin Mathieson ChemicalCorporation, East Alton, 11]., a corporation of Virginia 7 No Drawing.Filed Oct. 12, 1956, Ser. No. 615,501

10 Claims. c1. 52-5 This invention relates generally to propellentpowder and more particularly to an improved smokeless powderparticularly well adapted for use as the propellant in rockets and otherguided missiles.

Smokeless powder base propellants are utilized as the fuel in rocketmotors and guided missiles. The smokeless powder base is largelynitrocellulose that has been gelatinized by means of a suitablesubstantially nonvolatile solvent such as a plasticizer fornitrocellulose. This plasticizer may be a nonexplosive or it may be aliquid nitric ester of a polyhydric alcohol such as, for example,nitroglycerine. Propellants having this composition have a burning ratethat is influenced by the temperature at the time of ignition and by thepressure created: in the vessel or chamber in, which the propellant isburned. In other words, the pressure developed by a burning grain ofpropellant is proportional to the rate of burning which is influenced bythe temperature of the propellant when ignition occurs, and by thepressure at which the propellant burns. Because of the influence oftemperature and pressure on the burning rate of the propellant,propellants having a nitrocellulose base have not been entirelysuitable, heretofore, for universal utilicontaining such a lead saltwill burn at a constant rate over a range of pressure and with somevariation in This effect of the lead salts is known as the mesa orplateau effect and it is possible to prepare propellent powder withcustom built mesa effects. The burning rate over a given pressurerangecan be reliably predicted and propellants can be designed to burn at adesired rate at a particular pressure level by utilizing one or more ofthe lead salts to modify the burning characteristics of the grain.

It is, therefore, an object of the invention to provide a novelsmokeless powder propellant having burning characteristics that aresubstantially unaifected by variations in atmospheric pressure andpre-ignition temperature. A further object of the invention is toprovide grains of smokeless powder base composition having burning ratessubstantially independent of variations in pressure and ignitiontemperature over the range of pressures and temperatures at which suchpropellants are utilized. A more specific object of the invention is toprovide a propellant having novel mesa or plateau effects..-

j for nitrocellulose and particles of a lead salt of an ali-1 phaticorganic acid having more than six carbon atoms tially uniformlydispersing a lead salt of an alkoxy acid,

2,982,638 Patented May 2, 1961 and adapted to be dispersed uniformlythrough the gel and to retard variation in burning rate with change intemperature and pressure. More specifically, it has been found that asmokeless powder base grain having improved burning characteristics isproduced by substana lead salt of a keto acid, or a lead salt of anitrogen substituted amino acid in the nitrocellulose gel that is.

shaped into the propellent grain. Lead N,N di 2 ethylhexyl Baminopropionate, lead 12 ketostearate, which may be either the normal orbasic, lead 9(l0)- acetamidostearate, lead cyclohexylacetate, and leadbutoxyacetate are examples of the group of aliphatic organic acids thathave been found particularly advantageous for modifying the burningcharacteristic of the'propellent grain.

In order to determine the effect of the various ballistic modifying leadsalts of the aliphatic acids on the burning of the propellent grain, agrain of the desired composition is burned under a given pressure andthe burning rate is measured. The burning rate of the propellantprovided by this invention will increase rapidly with increase inpressure up to a'certain pressure level and then the burning rate willremain substantially constant over a range of pressure. For example, itwas found that a propellant having a nominal composition of about 57.8percentnitrocellulose, about 24.7 percent nitroglycerine, about 9.2percent triacetin, about 3.3 percent dioctylphthalate, about 1.7 percent2-nitrodiphenylamine and about 3.3 percent of one of the group of leadsalt ballistic modifiers indicated in the following table had asubstantially constant burning rate when burned at an external pressurebetween about 1000 and about 2000 pounds per square inch at atemperature of about 70 F. and F. as evidenced by the following results:

Pounds per square inch.

It can be seen from the foregoing table that the propellant provided bythis invention has a more uniform burning rate than one containing alead salt of an aromatic compound such as tetraphenyl lead over thepressure range of from about 1000 to about 2000 pounds per square inchwhich is the pressure range ordinaril encountered in practice. Thecomposition of the propellent grain can vary from .about 40 percent toabout 70 percent by weight nitrocellulose, from about 4 percent to about45 percent substantially non-volatile solvent for the nitrocellulose,from about 0.5 percent to about 5 percent of the lead salt ballisticmodifier, and from about 0.5 percent to about 2.5 percent of a suitablestabilizer for smokeless powder base propellants such as, for example,2-nitrodiphenylamine, diethyldiphenylurea, methylethyldiphenylurea,diphenylamine, or the like. In shaping the grain, it has been found thatfrom about 0.2 to about 0.5 part casting solvent per part ofnitrocellulose particles should be utilized to insure that the grainupon the simultaneous dissolution of nitrocellulose and solidificationof the, gel will be of substantially uniform composition throughoutcellulose.

the grains length. The solvent may contain from about 60 percent toabout 85 percent nitroglycerine or similar energizing modifier with thebalance being one of the class of non-explosive substantiallynon-volatile solvents hereinbefore described. A typical solid propellentgrain has the composition of about 58 percent nitrocellulose, about 25percent nitroglycerine, about 9 per cent triacetin, about 3 percentdioctyl phthalate, about 3.5 percent lead cyclohexyloxyacetate, andabout 1.5 percent Z-nitrodiphenylamine.

The propellent grain may be formed by any conventional extrusion orcasting process. With large grains, however, it is preferred and, insome instances it is mandatory, that the grains be shaped by a castingprocess. In one type of casting process suitable for the purpose,nitrocellulose base spherical pellets such as those formed by theprocess disclosed by Olsen et al. in US. Patent 2,027,114 may be placedin a suitable mold and the interstices between the pellets may then befilled with a substantially non-volatile solvent for nitrocellulose.

The contents of the mold are then heated to a temperatrue at which thepellets of gelatinized nitrocellulose will dissolve in the solvent andthe mass will set into a substantially homogeneous gel. The lead saltutilized to modify the burning characteristics of the propellent grainis incorporated in the gel either by incorporating it into the smokelesspowder pellets as they are formed or by dispersing the lead salt in thecasting solvent. Smokeless powder base pellets may also be made by theprocess disclosed in the Cox U.S. Patent 2,715,574 or by conventionalextrusion processes or any other suitable process. It is essential inorder to be able to consistently produce a propellant having apredetermined burning rate within a given pressure range that the leadsalt be well dispersed in the gel that constitutes the shaped propellentgrain.

A preferred casting solvent has the composition of about 72 percent byweight nitroglycerine, about 27 percent plasticizer and about 1 percentstabilizer, but the solvent may be varied in composition, and in someinstances it may consist of a plasticizer for the nitro- Anv suitablesubstantially non-volatile solvent fornitrocellulose may be utilized asthe solvent. Typical examples of such solvents are triacetin, dioctylphthalate, dibutyl phthalate, dimethyl phthalate, dimethyl sebacate,dibutyl succinate, dibutyl adipate, ethyl diphenyl phosphate, tributylphosphate, dimethyl phthalate, dioctyl sebacate, orthonitrobiphenyl,butyl benzyl phthalate, octyldiphenyl phosphate, triethylene glycol,di-Z-ethyl butyrate, and the like. .Best results are obtained with asolvent containing a liquid nitric ester of a polyhydric alcohol suchas, for example, nitroglycerine or nitroglycol. In many compositions,the major portion of solvent for the nitrocellulose may be one of theliquid explosive nitric esters of the polyhydric alcohols which areenergizing modifiers of the burning characteristics of the grain.

In order better to describe and further clarify the invention, thefollowing is a detailed description of one embodiment of a process formaking powder grains in accordance with this invention:

About 58 parts by weight nitrocellulose pellets formed by the processdisclosed by Olsen et al. in U.S. Patent 2,027,114 are placed in asuitable mold. The pellets were formed by suspending nitrocellulose inwater, dissolving the suspended particles in ethyl acetate, breaking upthe resulting lacquer into globules and removing the solvent from theglobules while they are suspended in water containing a protectivecolloid, such as, for example, gum arabic.

The mold is closed and about 42 parts by weight casting solvent made upof about 25 parts nitroglycerine, about 9 parts triacetin, about 3 partsdioctyl phthalate, about 3.5 parts lead cyclohexyloxyacetate, and about1.5 parts Z-nitrodiphenylamine are introduced into the mold underpressure and into the interstices between 4 the nitrocellulose pellets.then heated to about 60 C. and held at this temperature for about 48hours or until the casting solvent has dis-- solved the nitrocelluloseparticles and the mass has solidified without any solvent removal into ahomogeneous gel resulting suspension is poured into a mold having thedesired configuration. elevated temperature until the particles havedissolved The mold is then stored .at an and a gel has been formed. Thelead salt may be incorporated in the gel formed by this process or inany of the other processes by dispersing it in the nitrocelluloseparticles as they are formed or by dissolving it in the casting solvent.

The relatively constant burning rate, or plateau as it 'is commonlyreferred to in the art, will occur at different pressure levels as wasindicated in the foregoing table, depending upon which of the lead saltsis utilized. Moreover, the extent of the pressure range at which theburning rate will remain substantially constant will vary depending uponthe particular lead salt in the gel.

Although the invention has been described in considerable detail in theforegoing, it is to be understood that many variations may be made bythose skilled in the art without departing from the spirit and scope ofthe invention except as it is limited by the appended claims.

We claim:

1. A smokeless powder grain consisting essentially of gelatinizednitrocellulose and between about 0.5 percent and about 5 percent of alead salt of an aliphatic acid selected from the group consisting ofketo aliphatic acids, alkoxy aliphatic acids, acylamino aliphatic acids,and dialkylamino aliphatic acids. said lead salt having more than 6carbon atoms and being substantially uniformly dispersed throughout thegrain.

2. A smokeless powder grain consisting essentially of a propellentpowder base selected from the group consisting of nitrocellulose,nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, andbetween about 0.5 percent and about 5 percent of a lead salt of analkoxy aliphatic acid having more than 6 carbon atoms, said salt beingsubstantially uniformly dispersed throughout the grain.

3. A smokeless powder grain consisting essentially of a propellantpowder base selected from the group consisting of nitrocellulose,nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, andbetween about 0.5 percent and about 5 percent of a keto aliphatic acidlead salt having more than 6 carbon atoms, said salt being substantiallyuniformly dispersed throughout the grain.

4. A smokeless powder grain consisting essentially of a propellentpowder base selected from the group consisting of nitrocellulose,nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, andbetween about 0.5 percent and about 5 percent of a lead salt of anitrogen substituted amino aliphatic acid having more than 6 carbonatoms, said salt being substantially uniformly dispersed throughout thegrain.

5. A smokeless powder grain consisting essentially of a propellentpowder base selected from the group consisting of nitrocellulose,nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, andbetween about 0.5 percent and about 5 percent of a ballistic modifierselected from the group of lead salts of aliphatic acids having morethan 6 carbon atoms consisting of lead N,N-di-2-ethylhexyl 3aminopropionate, lead 12 ketostearate, lead 9(10)-acetamidostearate,lead cyclohexyloxyacetate, and lead butoxyacetate, said modifiers beingsubstantially uniformly dispersed throughout the grain.

6. A smokeless powder grain consisting essentially of The contents ofthe mold area propellent powder base selected from the group consistingof nitrocellulose, nitrocellulose-nitroglycerin, andnitrocellulose-nitroglycol, and between about 0.5 percent and about 5percent of lead N,N di 2 ethylhexyl- B aminopropionate dispersedsubstantially u n i f o r m l y throughout the grain.

7. A smokeless powder grain consisting essentially of a propellentpowder base selected from thegroup consisting of nitrocellulose,nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, andbetween about 0.5 percent and about 5 percent of lead l2-ketostearatedispersed substantially uniformly throughout the grain.

8. A smokeless powder grain consisting essentially of a propellentpowder base selected from the group consisting of nitrocellulose,nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, andbetween'about 0.5 percent and about 5 percent of lead9(10)-acetamidostearate dispersed substantially uniformly throughout thegrain.

9. A smokeless powder grain consisting essentially of a propellentpowder base selected from the group consisting of nitrocellulose,nitrocellulose-nitroglycerin, and

and about 5 percent of lead butoxyacetate dispersed substantiallyuniformly throughout the grain.

References Cited in the file of this patent UNITED STATES PATENTS2,498,388 Ball Feb. 21, 1950 FOREIGN PATENTS Canada Aug. 12, 1952 OTHERREFERENCES Colver: High Explosives, Crosby Lockwood and Son, London(1918), pp. 135, 169, 253 and 342. Copy in Scientific Lib.

1. A SMOKELESS POWDER GRAIN CONSISTING ESSENTIALLY OF GELATINIZEDNITROCELLULOSE AND BETWEEN ABOUT 0.5 PERCENT AND ABOUT 5 PERCENT OF ALEAD SALT OF AN ALIPHATIC ACID SELECTED FROM THE GROUP CONSISTING OFKETO ALIPHATIC ACIDS, ALKOXY ALIPHATIC ACIDS, ACYLAMINO ALIPHATIC ACIDS,AND DIALKYLAMINO ALIPHATIC ACIDS, SAID LEAD SALT HAVING MORE THAN 6CARBON ATOMS AND BEING SUBSTANTIALLY UNIFORMLY DISPERSED THROUGHOUT THEGRAIN.